Ultrasonic analysis and lock-in thermography for debonding evaluation of composite adhesive joints

Glass-fiber reinforced thermosetting plastic adhesive joints were characterized through ultrasonic imaging and lock-in thermographic analysis for assessing the adhesion quality before being subjected to static tensile mechanical tests and to accelerated aging cycles.The mapping of each sample has been obtained. Visual testing were performed on all specimens after the mechanical tests in order to obtain a comparison with ultrasonic and lock-in thermography technique.A quantitative analysis has been carried out to evaluate the ability of lock-in thermography in investigating inadequate bonding and obtaining the validation of the technique by the consistency of the results with the well-established ultrasonic testing.     

Nonlinear ultrasonic evaluation of the fatigue damage of adhesive joints

An experimental method based on the nonlinear ultrasonic technique is presented to evaluate fatigue damage of an adhesive joint. In this paper, specimens made from AZ31 magnesium–aluminum alloy bonded through an epoxy layer are subjected to a fatigue load. The ultrasonic harmonics generated due to damage within the adhesive layer are measured; and the acoustic nonlinearity parameter (ANP) based on the fundamental and second harmonics is determined. The results show that the normalized ANP increases with the fatigue cycles. Furthermore, a theoretical model with different interfacial compression and tension stiffness is proposed to interpret the generation of second harmonics.     

On laser welding of thin steel sheets

Abstract

This paper presents a process–structure–property relationship study of laser welds as a continuous consolidation method for joining thin monophased steel foils, thereby providing a more effective, less costly method to construct automotive catalytic converters. A body centred cubic (bcc) iron–chromium–aluminium alloy doped with Mischmetal was utilised in this study. Both pulsed and continuous wave modes were used to establish the limit welding diagrams for lap joint configuration. Actual laser welding parameters were selected using several testing conditions. The laser welds behaved substantially different from the base material under creep and high temperature oxidation. The difference was mainly attributed to the changes in grain morphology, precipitation of aluminium nitrides and carbides, and relocalisation of the reactive elements during liquid metal flow upon keyhole formation, solidification and cooling.     

金属板材液压胀形声发射检测

应用声发射技术检测了A3钢、20钢、45钢、406钢板材液压胀形全过程,所得数据表明液压胀形全过程存在两个屈服阶段,两次变形转移。第一阶段的屈服是凹模入口以内圆形区域金属的屈服,第二阶段的屈服是凹模入口以外筋板内环形区域金属板的屈服,说明凹模以外金属开始被拖动。第一次转移是由凹内向凹模外的环形区转移,第二次转移是环形区向中心区转移。胀形深度一声发射计数主经曲线有两个峰值区,两个平静区,第二个峰值的出现,表明凹膜入口以外的金属进入凹模内流动,第二个平静区预示着材料的破坏。     

Ultrasonic evaluation of the bonding strength of dissimilar metal bonds

Diffusion bonding of steel plates to titanium plates was carried out, and shear testing and ultrasonic measurement of bonds were performed to obtain the relationships between bonding strength, state of bonding interface and ultrasonic parameters. Fourier spectra of the ultrasonic wave reflected from the bonding interface were dependent on the state of the bonding interface; when an interlayer did not melt the spectrum showed a simple profile with one peak, and when the interlayer melted, the spectrum showed a profile with large irregularity. Transfer functions obtained from the spectrum were analysed with the subspace method (a kind of principal component analysis) and were represented by two major components. The bonding strength was quantitatively evaluated by two major components and a diameter estimated from the ultrasonic measurement.     

The reinforcing mechanism of carbon fiber in composite adhesive for bonding carbon/carbon composites

A carbon fiber reinforced adhesive was developed for bonding carbon/carbon composites. The Weibull distribution method was used to analyze the bonding strength data, and the results showed that when the volume fraction of carbon fiber was 6 vol.%, the Weibull modulus was 42.9393 and the bonding strength of the adhesive was 11.3763 MPa. A model was proposed to explain the reinforcement of carbon fiber, and it was found that the strength of adhesive was a cubic function of the volume fraction of carbon fiber, and the function model was consistent with the Weibull data. We investigated that the carbon fiber could bridge adhesive matrix as a bridging effect for releasing the residual stress and inhibiting the extension of micro-crack.     

Alternating current-gas metal arc welding for application to thin sheets

The metal transfer in alternating current-gas metal arc welding (AC-GMAW) was analyzed in order to predict the drop size. The effects of complex waveforms of the process, involving both the electrode positive (EP) and the electrode negative (EN) pulse regions, were investigated analytically. The force-displacement model was modified to predict the drop size in AC-GMAW. Experiments were conducted using different types of wires for validating the predicted results. The effect of EN pulse parameters on the drop size was modeled, eliminating the need for experimental trial and error. The drop size information can be used to predict the range of the joint gap that can be bridged effectively. The proposed technique was found to be equally applicable to both direct current-gas metal arc welding and P-GMAW.     

Fabrication and adhesive properties of thin organosilane films coated on low carbon steel substrates

We investigated the fabrication and adhesive properties of thin organosilane films coated on the surface of low carbon steel substrates by curing γ-glycidoxypropyltrimethoxysilane (γ-GPS) solutions hydrolyzed in different solvents. This method appears to be a promising alternative treatment for the chromium and phosphate mainly due to its excellent corrosion protection and adhesion properties to organic coatings and a non-toxic pretreatment. In this work the elemental distribution in γ-GPS films coated on low carbon steel substrates was analyzed by an energy dispersive X-ray spectrometer (EDX), and the effect of curing temperature and solution concentration on the chemical structures of this silane was also carried out with reflection-absorption infrared (RAIR) spectroscopy. We systematically investigated the processing variables regarding adhesive strength of the film, including hydrolysis solvents, hydrolysis time, solution concentration and curing temperature. Compared with other experimental conditions, the present results provided a consistent demonstration that γ-GPS films exhibited improved adhesive strength to metal substrates in case of using DI water/methanol mixture as hydrolysis solvent, hydrolysis time of 48 h, solution concentration of 10%, curing temperature of 150 °C and curing time of 1 h. The fracture mode of γ-GPS films varied with different deposition parameters.     

Analysis of plastic bending of adhesive-bonded sheet metals taking account of viscoplasticity of adhesive

The present authors proposed a new technique of plastic bending of adhesive-bonded sheet metals. In this process, large transverse shear deformation occurs in the adhesive layer, which in some cases would induce the geometrical imperfection (so-called ‘gull-wing bend’) and the delamination. Since the strength of the adhesive is highly rate-sensitive, the amount of shear deformation of the adhesive layer and, as a result, ‘gull-wing bend’, are strongly influenced by the forming speed. In the present work, the effect of forming speed on the deformation characteristics of adhesively bonded aluminium sheets was investigated by performing V-bending experiments with various punch speeds at room temperature. In order to discuss the effect quantitatively, the numerical simulations for the bending were also conducted using a rate-dependent constitutive model of plasticity for the adhesive. Consequently, it was found that the large shear deformation and ‘gull-wing bend’ are suppressed by high-speed forming since the deformation resistance becomes higher at high strain rate.     

An experimental method for determining ductile tearing energy of thin metal sheets

This paper presents a few typical experimental methods for determining the value of tearing energy under a simple plane stress condition and proposes a novel one for it. In this method, several unixaial tensile tests were conducted with test specimens of various lengths. It was assumed that, for each test, the total energy required to tear the specimen can be decomposed into two parts: one associated with tearing (including the plastic deformation in the vicinity of torn cross section) and the other with the plastic deformation over the whole working volume of the specimen. Consequently, when plotting the total energy divided by the specimen width and thickness against the working length of the specimen, a straight line was obtained. The intercept of this line gives the value of tearing energy, corresponding to a zero length specimen. For mild steel, this value was found to be 1520 kJ/m². Comparisons were made between the present result and those by other test methods.     

金属磁记忆检测数据处理系统

阐述了开发金属磁记忆检测数据(MMM)处理系统的必要性,并基于VB开发了一套功能强大的金属磁记忆检测数据处理系统,详细介绍了该系统的主要功能特点和各个功能模块的应用.     

Applicability of adhesive–embossing hybrid joining process to glass-fiber-reinforced plastic and metallic thin sheets

Adhesive–embossing hybrid joining process was applied to A2017P and three types of glass-fiber-reinforced plastic (GFRP) thin sheets. Optical microscopy shows that a sound A2017P–thermosetting GFRP hybrid joint without crack/delamination in the composite or adhesive failure can be produced by optimizing adhesive thickness, embossing stroke and embossing temperature. The results of tensile shear test indicate that the optimally hybrid-bonded A2017P–GFRP joint exhibits improved load carrying capability, slip displacement and better energy absorbing characteristics than the adhesively bonded joint when subjected to tensile loading. This investigation shows that the adhesive–embossing hybrid joining process is a competitive alternative joining method for the fabrication of ultra lightweight thermosetting GFRP-metal hybrid structures and has great potential for wider applications, which is attributed to its benefits in terms of joining properties, operation simplicity, weight-cost effectiveness and recyclability.     

Adhesive wear in deep drawing of aluminum sheets

This paper focuses on the experimental validation of the common model for adhesive wear initiation by Czichos et al. for conventional aluminum deep drawing operations. A strip drawing test with a 90° bending process is used for the studies. The local contact conditions at the drawing edge are examined by analytical examination and numerical simulation on different degrees of refinement. Contact normal stresses and temperature profiles are investigated and correlated with the experimental observation of adhesive wear.     

Hybrid joining process for carbon fiber reinforced thermosetting plastic and metallic thin sheets by chemical bonding and plastic deformation

A new joining process for thin metallic and continuous carbon fiber reinforced thermosetting plastic (CFRP) sheets is proposed. This joining process is a hybrid of chemical bonding and plastic deformation, usable for ultra-lightweight structures. In contrast to conventional joining methods, such as rivet joining with an adhesive, the proposed method does not require any additional components and can eliminate holes that would cut the continuous carbon fibers and cause stress concentration. Hence, a smaller weight and a higher joining quality can be attained, especially for thin sheets. Aiming at making comparison and demonstrating the applicability of the proposed hybrid joining method, two thermosetting CFRP sheets with different laminates were used as lap adherends in the experiment. The effects of the deformation temperature, the use of a dummy sheet and the relative positions of the sample and dummy sheet on the joining quality were systematically investigated and optimized. The optimal hybrid joint shows high-quality bonding without delamination or adhesive failure. The tensile shear test of single-lap A2017P-CFRP hybrid joints manufactured under optimal experimental conditions indicates that, compared with adhesive bonding and conventional rivet joining with an adhesive, the proposed joining method has obvious superiority in terms of tensile shear load, slip displacement and absorption energy.     

Characterization of adhesive bond properties using Lamb waves

This research combines laser ultrasonic techniques with the two-dimensional Fourier transform (2D-FFT) to characterize adhesive bond properties. The experimental procedure consists of measuring a series of equally spaced, transient Lamb waves in specimens consisting of aluminum plates joined with an adhesive bond. The frequency spectrum (dispersion curves) for each specimen are obtained by operating on these transient waveforms with the 2D-FFT. This study quantifies the effect of bond stiffness on the dispersion curves of two different bonded specimens (a single aluminum plate with an adhesive transfer tape attached to one side, and two aluminum plates joined with the same adhesive tape) and four adhesive bond conditions (un-aged, and three different aging temperatures and times). The proposed procedure consists of first determining the frequency spectrum of the Lamb waves that propagate in each of the two bonded specimens (plus a single plate); these measurements provide the dispersion curves for each specimen in their un-aged state. Degradation causes changes in the stiffness of an adhesive bond, which causes changes in the dispersion curves of the aged specimens. Experimentally measured dispersion curves are used to quantitatively track changes in the bonded specimens, as a function of age. Finally, these experimental results are interpreted in terms of an analytical model that replaces the adhesive bond layer with a linear spring boundary condition.     

Rigid-plastic and elastic-plastic finite element analysis on the clinching joint process of thin metal sheets

This article describes the joining of thin metal sheets by a single stroke clinching process. Elastic-plastic and rigid-plastic finite element analysis were applied by employing Coulomb friction and constant shear friction in order to investigate the behavior of the clinch joint formation process. Four process variables, such as die diameter, die depth, groove width, and groove corner radius were selected to investigate the parametric effect on the clinch joint. The strength of clinch joints were evaluated by examining the separation strengths, such as peel strength and tensile shear strength, respectively. A failure diagram was constructed that summarizes the analysis results. The simulation results showed that die diameter and depth were the most decisive parameters for controlling the quality of the clinch joint, while the bottom’s thickness was the most important evaluation parameter to determine the separation strengths.     

Pre-treatment by dry ice blasting for adhesive bonding

In recent years, the constant development of adhesives and coatings has contributed to the establishment of the adhesive and coating technology in several fields. Based on findings in macro-molecular chemistry, the cohesive strength, e.g. the internal strength of adhesives, has been enhanced continuously. In contrast to the adhesive strength, the mechanical, chemical and physical adhesion, the cohesive strength is relatively strong. As a consequence, adhesion is usually the weakest link of an adhesive bond, thus, most often it is adhesive fracture that can be observed. Pre-treatment and the use of so-called coupling reagents represent an approach to improve the adhesive strength. The paper presents dry ice blasting as a pre-treatment process and a process model with which the reasons for the increased adhesive strength can be clarified. With respect to the relevant blasting parameters, the effects of a pre-treatment with dry ice blasting on roughness, surface topography, specific surface, mechanical activation, surface energy and chemical composition depending on relevant parameters have been determined.     

纳米氧化铜对磷酸盐胶黏剂耐水性能的影响

以H3PO4和Al(OH)3为基体,纳米氧化铜为填料来制备磷酸盐无机胶黏剂。胶黏剂粘结的莫来石片,在人工海水中浸泡168 h后,测试其剪切强度,并以此强度为标准,来探究纳米氧化铜的加入对磷酸盐胶黏剂耐水性能的影响。研究结果表明,纳米氧化铜可以有效改善粘结剂的耐水性能,并且当加入量为基体的20%(质量分数,下同)时,经150℃处理的莫来石粘结片浸泡在人工海水中168 h的抗剪切强度最高,为7.13 MPa;莫来石粘结片经1300℃处理后,浸泡在人工海水的抗剪切强度最低,为2.31 MPa;发现经煅烧处理的纳米氧化铜相比未煅烧处理的氧化铜可以更好地提高粘结剂粘结强度。     

Relation between acoustic emission analysis during cure cycle and bonded joints performances

In 1993, a research program was started and developed in JRC Diagnostic and Reliability laboratories to assess the possibility to predict the structural behaviour of adhesive joints monitoring acoustic emission (AE) during the cure cycle leading to their production. Cure cycles have therefore been performed, either respecting the standards and guidelines established for the adherent materials, adhesive layer, timing, temperatures, or instead modifying one or more of these factors. The latter situation would presumably produce a joint which is unsuitable for use or at least with non-ideal characteristics. The idea was that acoustical activity during the different cycles should be discernible from a statistical point of view, presenting a relation with the quality of the joints finally produced. From experimental data some evaluation criteria were sorted out and a possible outlining of on-line joints’ quality control through AE concepts is provided.     

Process optimization for elastic adhesive bonding of large components with high tolerances

The technology of elastic adhesive bonding is utilized very often to join large components. Due to economic reasons large work pieces normally feature high tolerances and thus have to be adjusted geometrically. During that deformation process strains arise inside the work piece. These can lead to debonding caused by relaxation processes if the force of the strains is higher than the adhesive strength. Therefore the attainable quality of the adhesive bonding process often is reduced significantly. Hence a method to enhance the quality and flexibility for the elastic adhesive bonding of large components with high tolerances is needed. The main improvement of the methodology presented in this paper is an innovative algorithm for the optimized alignment of one component to another component, which is based on the actual distances between the work pieces and considers the emerging stresses inside the work piece due to the deformation also.